Cerium oxide powder, which is a high functional ceramic material, has been widely used as a catalyst, a phosphor, cosmetics, an abrasive, etc. Recently, cerium oxide powder has received much attention for its use as an abrasive for a CMP (Chemical Mechanical Polishing) process in the field of semiconductor device.
In general, the cerium oxide powder can be prepared by a liquid-phase method, a gas-phase method or a solid-phase method.
According to the liquid-phase method, a pH control agent such as ammonia is added to a starting material, e.g., a trivalent or tetravalent cerium salt to prepare cerium oxide directly from cerium salt. This method is economically advantageous because the cost for raw materials and equipment is comparatively lower than other known methods. Nevertheless, it is difficult to control particle growth in this method because a reaction between starting materials easily occurs from the nucleation stage. Furthermore, fine cerium oxide prepared by the liquid-phase method is not desirable as an abrasive because of its low the polishing rate, which is disadvantageous for a continuous process and it decreases productivity.
According to the gas-phase method, a cerium metal salt precursor is vaporized and then bonded with oxygen, etc. to directly prepare cerium oxide. This method includes flame combustion decomposition, gas condensation decomposition, plasma vaporization, laser vaporization, etc. However, this method has difficulty in terms of mass production of cerium oxide powder because the cost of cerium metal salt precursors and equipment is high. Furthermore, this method is still under study.
Meanwhile, in the solid-phase method, a precursor material is fired at high temperature to prepare cerium oxide. Cerium carbonate is widely used as the precursor, and the physical properties and shape of cerium oxide can be varied depending on the structure and/or shape of cerium carbonate used. Thus, in order to control the physical properties (for example, abrasiveness of cerium oxide, etc,) or shape, etc. of cerium oxide, a method for preparing cerium carbonate, which can easily control the structure or shape of cerium carbonate, is required.
However, a method for preparing cerium carbonate with a certain structure or shape by using a simplified process has not been adequately developed yet, and particularly, there is a continuing demand for a method capable of preparing hexagonal cerium carbonate by a more simplified process.
Moreover, a method for preparing cerium carbonate known so far has a disadvantage of insufficient yield or productivity. In addition, to produce cerium carbonate with a specific shape or crystal structure such as a hexagonal structure, this method requires a high pressure reaction, which raises safety concerns.